If WordPress Connect fails, check these in order:

1. The Hub URL is https (or localhost for a local preview).
2. Site ID and Site key are the current pair from the Connect your site card. If you lost the key, click Show or Generate a new key there.
3. The site can reach the Hub over HTTPS. A firewall or DNS issue on the host will fail the handshake.
4. The plugin version is the current zip from this Hub. In WordPress: Plugins, Add New, Upload Plugin, then Replace current with uploaded.

We never email the Site key. How to connect or Update the plugin zip.